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Case study: Calling Electric hybrid bluff (or Supremacy) using real world example

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saini flyer

Well-Known Member
Joined
Mar 12, 2010
Messages
503
Location
Dallas, TX
Full disclosure(please read in fine print): Some numbers are close approximations.

I am tired of the numerous hybrid aircraft threads. I say its time to call the bluff of all electric hybrid proponents. I went ahead and did a real example with real numbers to compare electric hybrid against our beloved half a century old ICE. Below is a partial list of what I see reflected back again and again about electric hybrid powerplant,
  1. It will have exceptional Reliability...the most talked aspect of electric as there are two bearings that move in a motor vs a zillion in ICE
  1. Doesn’t require an extension chords please…..how do you solve the battery capacity/weight/cost problem
  1. It will have overall weight savings…….always debated…. I want to end this one!
  2. It will have lower operating costs… Operation+Maintenance+Misc
  3. It will be better in engine out scenario than a conventional ICE….maybe make it uneventful!
  4. Quieter when flying around…
  5. There is more but let me start with these first…………...
I added some of my own constraints so I can do an apples to apples comparison,
  1. I do not want to build a new aircraft from scratch that takes the perceived advantage of hybrid
  1. I will start with very good existing aircraft with more than 100 flying, still in production, with great factory support.
  1. I wont change anything on existing aircraft in terms of Structure & Aerodynamics.
  1. I will stick to the power requirements of the existing aircraft
  2. I will use off the shelf stuff that an average Joe can order and buy rather than some development project or shady business product
  1. There must be cost savings….. almost from get go
  1. There must be cost savings over time

I choose RV10 as the aircraft of choice. It is a real 4 seater plane. Those who want to complain about starting with a 2 seater, please pull down the backseats and make it a two seater but if I start with a two seater, I cant make a 4 seater out of it. The numbers and $$ should scale nonetheless for a two seater too. Here are some performance and specifications that I will work with,

  1. HP: RV10 works from 210hp(two at the factory) to 260HP(only one at the factory). So this is my required HP for a hybrid: https://en.wikipedia.org/wiki/Van's_Aircraft_RV-10
  1. FWF weight: Weight The FWF weight is about 500 lbs+ so the hybrid needs to be less than this complete.
  2. Cruise: At 65% on 210hp &8000' the cruise is 175mph, so the hybrid should cruise at this spec:Van's Aircraft - RV–10 Performance
  1. Range: The range of 1000 miles at the above power point needs to be met by the hybrid too.

Below is my description of electric hybrid FWF for RV10 (I can buy everything today) that I replace from the current 360ES/IO540,

ICE for hybrid: Turbocharged EI, Rotax 135HP [I can buy it today from Arthur at Trendek(Gyroplanes Gyrocopters Gyroplane Gyrocopter wiatrakowce |) or from Ceilier aviation (Home) or wait until 2017 for the official Rotax release]. The weight is 185lbs installed. The cost is about $28k but assume $40k when Rotax releases it in 2017 :(

Electric motor for hybrid: Two 40hp (total 80HP) coupled together Axtera's Emrax based parallel hybrid powerplant: axter aerospace – Innovación aeronáutica en electrónica de control, potencia y seguridad. The weight of one powerplant is between 80-100 lbs. So I will assume 200 lbs for two. This includes everything (motor+controller+Batter+BMS+charger+wire harness+ readout gauge).The cost is $21k each at a $42k combined… steeeepppp!

Let me compare the performance numbers of the electric hybrid:

  1. HP: Both of these powerplant combine together to give you a 135+80=215 HP total power. This is inline with the RV10. Also this is a turbo Rotax so density altitude is not a big deal. The electric motor doesn’t care about density altitude and gives you same HP irrespective. Just as an example the IO540 at 5000' elevation is only a 220HP engine anyways. In fact, If I am at 8000' elevation the IO540 is only making 198HP and electric hybrid powerplant is still producing 215HP. The electric is winning already in certain situations!

  1. FWF weight: IO540 is 500lbs Vs hybrid at 185(Rotax)+200(Axtera)= 385 lbs. The electric is winning (100lbs+) here hands down!

  1. Cruise: At 65% & 8000' the NA 210HP ICE makes about 103HP. The turbo Rotax at 75% power makes 101HP at 8000'. The calculated cruise is 174 mph. I call the hybrid even with the IO540 performance unless 1mph is huge difference in your book!

  1. Range: The 60 gallon tank with Rotax gives you 1700 miles(6gph) range vs the 1000miles(11.5 gph economy cruise) of ICE. For the similar range of ICE @ 1000 miles I only need to carry 35 gallon and save weight of 25 gallon( 150 gallon). The hybrid wins hands down.

Here are the added advantages:
  1. I have a twin(or a three engine) aircraft with centerline thrust for exceptional reliability in case of ICE failure.
  2. Even though I have two separate engines, my pilot rating is single engine and so is my plane….. Excellent :)
  3. I am not carrying additional weight of a conventional twin on the wing and not making the airflow dirty form the engine installation either…..again an added benefit!
  4. I do not have a draggy windmilling prop or a stationary prop in case of engine out.
  1. How far to the crash site?…….The approach speed of RV10 is 65knots(75 mph) and if you loose your ICE, all you need is ~8HP/6KW power(yes that is not a typo..) to keep the plane flying at 75mph. So a 6KWhr battery pack is good to fly for an hour. You get two of these in the Axtera with two electric motors. So you can fly on electric alone for almost two hours. Even if you consider half of the battery power drained out for climb, you can still fly for an hour. I think I will fly quite electric most of the time :)
  2. Jarno(please help) will add the calculation for ROC on 80HP Emrax alone installed in RV10 but Axtera suggests that for< 750 Kg (1650 lbs) gross with the high torque the ROC is is 200fpm. I am assuming the same for a two motors and 2700lbs all up weight of RV10.
  3. The 74" prop is already quiter(at low rpm) but you can go all electric after the climb out for the next $100 hamburger for < $2 total fuel cost. Even buying new battery pack every 1000hr of flight time is only $5/hr added cost. I finally live in a time where that Hamburger is more expensive than my fuel cost to get there.
  1. The overhaul cost, maintenance cost of the ICE in both cases might be the same. Air cooled is simple but parts are expensive, Rotax is complicated but I assume a complete overhaul is $12k at most. The TBO is same for both but my TBO for flying hours will be substantially different as I will fly electric most times.
  1. There is also an option to use a cruise prop rather than a constant speed prop as my HP is constant for my hybrid. I also save on weight.
  2. Did I mention lower operating costs?
  3. Payload: At 1200lbs without fuel &+ 100 lb gained from hybrid FWF-35gal fuel for 1000 mile range(210 lbs)=1090 lbs. This is no longer 4 full American adults but almost entering the six seater aircraft payload numbers. The twin engine Aerostar I flew last is a six seater with 1250lb payload after full fuel for a 800 mile range flying at 200mph.
  4. Upfront FWF cost: Cost of Axtera system at $21k*2=$42k+ $28k(Rotax)= $70k. A far cry from being cheap. It beats the IO540 by a lot but At 11.5gph 100LL at $5 Vs 6 gph Mogas @ $2.5 within the first year of flying 150 hrs, I save $6.4k. If most of my flying is local except for the long cross country cruise. I can reduce the Rotax RPM for an even better fuel economy, or as I said go electric all the way…. At $6.4k fuel saving, it will take at least three years before the upfront cost is recouped.

If I do the same for a two seater LSA with the right hybrid powerplant, I should get the same results. Physics is the same and numbers cant lie. Please also see that this is a parallel hybrid and not a series hybrid. In my opinion, the advantages of a series hybrid lies in non conventional design. It could be truly disruptive in performance.

This is what can be done today, with stuff I can buy now. Electric hybrid cant come on top in every situation(& has limitation like climb out restricted to a few minutes). It is not for everyone but for me this evaluation was good enough to see that it shines at all the critical phases and by now you know where this is going………….
 
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